When boring holes deep into the earth, it is common to employ a slush pump to remove slush, mud and other liquid debris from the drilling hole. Such slush pumps, due to their highly abrasive work environment, require frequent repair and inspection. For this reason, it is necessary to provide the slush pump with easily accessible and removable internal components.
Slush pumps of this type commonly include spring biased valves which matingly engage and seal against the valve seat surface of an associated valve seat for regulating the fluid flow through the pump. In the prior art, slush pump valve seats are of two types: either a full open type or a crossarm type; the distinction between the two types being the absence or presence of special valve guiding structure in the flow passage. The full open type valve seats are characterized by an unobstructed internal flow passage. The prior art crossarm type valve seat are characterized by a plurality of arms disposed in the internal flow passage which support an axially positioned valve stem guide.
During extraction of the prior art valve seats from a slush pump for inspection or replacement, one type of removal tool is employed for extracting a full open type valve seat and another type of removal tool is required for extracting a crossarm type valve seat. More specifically, the full open type seat is extracted from the slush pump by inserting a removal tool completely through the internal flow passage. The removal tool emerges through the bottom of the full open valve seat and is then hooked underneath the bottom and pulled upwardly until the valve seat becomes dislodged from the slush pump. The crossarm type valve seats are extracted from the slush pump by inserting into the flow passage a removal tool which, in contradistinction, is hooked underneath each of the arms and then urged upwardly against the arms in the flow passage to dislodge the valve seat from the slush pump. The removal tool used for the full open type valve seats is incompatible with the crossarm type valve seats as the arms and valve guiding structure in the flow passage prevent the removal tool from being inserted completely through the flow passage to hook underneath the seat. Likewise, the crossarm type removal tool is incompatible with the full open type valve seats in that there are no arms in the flow passage under which the tool may hook.
Because of the extremely large force, typically in the order of several tons, which is required to dislodge a valve seat from the slush pump, the arms of the crossarm type valve seat must be of sufficient structural integrity to withstand the removal process. In other words, a dilemma is presented for the engineer in that the arms must have a large enough cross-section to provide adequate strength to withstand the removal process, but not so large as to overly restrict the fluid flow through the valve seat.
Therefore, due to the practical realities of removing a valve seat from a slush pump, there has heretofore never been provided a valve seat assembly including a centrally located valve stem guide supported by arms of very slim profile wherein fluid flow impedance through the valve seat member is minimal.